Inj duty cycle too high?

[Bruce Melton]

I just tuned a 02 Z06 with just headers and intake. Got the LTFT in line after lean log by IFR adjustment. (now in 0>-6 range). On dyno, tuned PE to ~13 AFR but--- stock 28 lb injectors show 102% max duty cycle, 20% avg, 20.7 PW, .43 Calc flow on dyno pull.
This seems extreme for a car that put down 372 hp.
Any thoughts ???
TIA,
Bruce

[TAQuickness]

I just tuned a 02 Z06 with just headers and intake. Got the LTFT in line after lean log by IFR adjustment. (now in 0>-6 range). On dyno, tuned PE to ~13 AFR but--- stock 28 lb injectors show 102% max duty cycle, 20% avg, 20.7 PW, .43 Calc flow on dyno pull.
This seems extreme for a car that put down 372 hp.
Any thoughts ???
TIA,
Bruce


I'm not the biggest fan of adjusting the IFR to get trims/WB readings inline. I would think to get accurate IDC readings, you would need the IFR table to be accurate.

102% IDC indicates you need bigger injectors.

[Bruce Melton]

I'm not the biggest fan of adjusting the IFR to get trims/WB readings inline. I would think to get accurate IDC readings, you would need the IFR table to be accurate.

102% IDC indicates you need bigger injectors.


I know it is too high, but is there something I did that could likely cause this?

Never seen stock internals LS6 use this much fuel--It is a very low mile car (15k) in great shape.

[dfe1]

The real question is whether duty cycle numbers are actual or theoretical. I've never worried much about duty cycle, I look at pulse width. A general rule of thumb is that maximum pulse width with a sequential EFI system is 20 milliseconds at 6,000 rpm-- that's based on the amount of time available. 6000 rpm= 100 revs per second. Each injector fires once per two revolutions which equals 50 injector cycles per second. One second is the equivalent of 1,000 milliseconds, which divided by 50 equals one firing every 20 milliseconds. That doesn't take into account injector opening and closing time, so realistically, there's only 16-17 milliseconds of actual injector on time available. If your injector pulse widths are less than the maximum time available at a particular rpm, you should be fine. Something else to consider, if you need an actual pulse width that exceeds the time available, the engine will run lean. In any event, you mention a 20.7 ms pulse width, so as TAQuickness notes, you need larger injectors.

[redhardsupra]

I'm not the biggest fan of adjusting the IFR to get trims/WB readings inline. I would think to get accurate IDC readings, you would need the IFR table to be accurate.

102% IDC indicates you need bigger injectors.

you will never know what the car really wants until your configuration of software will reflect hardware (IFR, VE) and your desired settings (PE) achieves a consistant goal (AFR). then and only then you will know how your injectors are doing. my bet is however you're too close for comfort, so i'd put something bigger in there. there's been a lot of 42s floating around on forums for ~200bux lately, which is a great deal. highly recommend them

[Bruce Melton]

you will never know what the car really wants until your configuration of software will reflect hardware (IFR, VE) and your desired settings (PE) achieves a consistant goal (AFR). then and only then you will know how your injectors are doing. my bet is however you're too close for comfort, so i'd put something bigger in there. there's been a lot of 42s floating around on forums for ~200bux lately, which is a great deal. highly recommend them

My question is really why is this particular car so thirsty? Usual the duty cycle is in the upper 80s with these intake/header LS6s. This one was quite lean and it took lots of fuel to get the LTFTs in line and then it was running high 11s mid 12s AFR till I PEed to 13. The overall result was these unusually high duty cycles.

Adding ~15% IFR was required to get the LTFTs out of the +10>15 range.

[redhardsupra]

My question is really why is this particular car so thirsty? Usual the duty cycle is in the upper 80s with these intake/header LS6s. This one was quite lean and it took lots of fuel to get the LTFTs in line and then it was running high 11s mid 12s AFR till I PEed to 13. The overall result was these unusually high duty cycles.

Adding ~15% IFR was required to get the LTFTs out of the +10>15 range.
and my point really is that you can't make such judgements until you know everything you're measuring is right. it's like gauging how late you are by looking at a clock that you know is not right, but you don't know by how much.